Fixing device ensuring smooth delivery of sheet

Abstract

A fixing device includes a fixing member, a pressure member, and a guiding member. The guiding member includes a first guide surface, a second guide surface, and a pair of third guide surfaces consecutively installing both end portions in the axial direction of the first guide surface and both end portions in the axial direction of the second guide surface. The first end edge of the first guide surface has a first circular arc shape arranged such that a center portion in the axial direction projects toward the downstream side in the rotation direction with respect to both end portions in the axial direction. The second guide surface is one of a curved surface in a second circular arc shape arranged such that a center portion in the axial direction is close to the first circumference surface with respect to both end portions in the axial direction.

What is claimed is: 
     
       1. A fixing device for performing a fixing process on a sheet including a first sheet surface on which a toner image is formed, the fixing device comprising:
 a fixing member that includes a first circumference surface, the fixing device being configured to rotate the fixing member in a predetermined rotation direction, the fixing device being configured to bring the first circumference surface into contact with the first sheet surface; 
 a pressure member that includes a second circumference surface, the fixing device being configured to press the pressure member against the first circumference surface of the fixing member so as to form a fixing nip portion through which the sheet passes between the pressure member and the fixing member, the fixing device being configured to bring the second circumference surface into contact with a second sheet surface on an opposite side of the first sheet surface; and 
 a guiding member arranged at a predetermined distance from the first circumference surface, the guiding member being configured to bring the sheet into abutting contact with the first circumference surface of the fixing member and then guide the sheet to the fixing nip portion; wherein: 
 the first circumference surface of the fixing member is constituted to have a smaller outer diameter of the center portion in an axial direction during the rotation than outer diameters of both end portions in the axial direction; and 
 the guiding member includes
 a first guide surface that includes a first end edge arranged to face the first circumference surface, the first guide surface being located to extend toward the first circumference surface at an upstream side of the fixing nip portion in the rotation direction, the first guide surface being configured to guide the sheet to the first circumference surface, 
 a second guide surface at a downstream side of the first guide surface in the rotation direction, the second guide surface being consecutively installed on the first guide surface to intersect with the first guide surface in a center in the axial direction of the first end edge, the second guide surface being arranged along the first circumference surface, and 
 a pair of third guide surfaces consecutively installing both end portions in the axial direction of the first guide surface and both end portions in the axial direction of the second guide surface, wherein 
 in a view from a direction perpendicular to the first guide surface, the first end edge of the first guide surface has a first circular arc shape arranged such that a center portion in the axial direction projects toward the downstream side in the rotation direction with respect to both end portions in the axial direction, and 
 when the second guide surface is viewed from a direction along the second guide surface from the upstream side in the rotation direction, the second guide surface is one of a curved surface in a second circular arc shape and a planar surface, the second circular arc shape being arranged such that a center portion in the axial direction is close to the first circumference surface with respect to both end portions in the axial direction. 
 
 
     
     
       2. The fixing device according to  claim 1 , wherein:
 the second guide surface includes a curved surface having the second circular arc shape; and 
 the second circular arc shape has a curvature radius larger than a curvature radius of the first circular arc shape. 
 
     
     
       3. The fixing device according to  claim 1 , wherein:
 in a cross-sectional view intersecting with the axial direction, a second angle formed by the first guide surface and the third guide surface in both the end portions in the axial direction of the first end edge is larger than a first angle formed by the first guide surface and the second guide surface in the center in the axial direction of the first end edge. 
 
     
     
       4. The fixing device according to  claim 1 , wherein:
 the first circular arc shape has a curvature radius equal to or more than 2000 mm and equal to or less than 4000 mm. 
 
     
     
       5. The fixing device according to  claim 4 , wherein:
 the second guide surface includes a curved surface having the second circular arc shape; and 
 the second circular arc shape has a curvature radius equal to or more than 5000 mm. 
 
     
     
       6. An image forming apparatus, comprising:
 an image forming unit configured to form an image on a sheet; and 
 the fixing device according to  claim 1 .